Clamp for precision cutting tool

ABSTRACT

Apparatus for precision cutting of sheet material (e.g. nonferrous metals such as aluminum, brass, asbestos board, or the like), comprising a work-support table, displacement-sensing means mounted along two adjacent sides of said support table and a novel quick-clamping means for holding a workpiece against said table. The quick-clamping means has an elongate clamp bar along each side of the cutting tool, these elongate bars comprising biased means therealong for compensating for differences in thickness along the length of said workpiece.

United States Patent Baker 5] Nov. 11, 1975 [5 1 CLAMP FOR PRECISIONCUTTING TOOL 2.506.436 5/1950 Seybold 269/32 '7 '7 Inventor: J n w. a 4achusetts Dri e, 3.199.860 8/1965 Moherg -69/87...

' west Acton Mass' 0171) Primur E.\'an1inerRoy Lake [22] Filed: Apr. 26,1974 Assistant E\'uminer- -Mark S. Bicks Attornev. Agent, or Firm-RobertA. Cesari; John F. 21 A l. N 7 L l 1 PP O 464 4 4 McKenna; Andrew F.Kehoe Related US. Application Data [62] lgh'isionn of Ser. No. 273385.July 20. 1972. Pat. No. [57] ABSTRACT Apparatus for precision cutting ofsheet material (e.g. U S Cl 269/87 769/366 nonferrous metals such asaluminum, brass, asbestos m g board, or the like), comprising awork-support table. [58] Fie'ld 163 265 displacement-sensing meansmounted along two adja- "769/766' i, 5 cent sides of said support tableand a novel quickclamping means for holding a workpiece against saidble. The quick-clamping means has an elongate [56] References Citedclamp bar along each side of the cutting tool, these UNITED STATESPATENTS elongate bars comprising biased means therealong for 816.5293/1906 Burt 269/872 mpensating for differences in thickness alongthel.5l9.2 5 l2/l924 Tnvns d 269/265 l.942.728 l/l934 Perlsteiil 269/275length of Sam workplece. 2.166.998 7/1939 Morgan 269/32 7 Claims, 9Drawing Figures l r- I l E Z: SG

Sheet 1 of 3 US. Patent Nov. 11, 1975 US. Patent Nov. 11, 1975 Sheet 2013 if 111 I *1 v 7 US. Patent Nov. 11, 1975 Sheet3of3 Fig.3.

CLAMP FOR PRECISION CUTTING TOOL This is a co-pending divisionalapplication divided out of U.S. Ser. No. 273,385 filed on July 20,1972now U.S. Pat. No. 3,820,233. The copending divisional application isU.S. Ser. No. 464,475 filed on Apr. 26, 1974.

BACKGROUND OF THE INVENTION This invention relates to apparatus usefulfor rapidly cutting sheet material to a high precision tolerance byutilizing dimension-monitoring sensors associated with a work table anda quickly-actuatable clamp means for holding the workpiece againstthetable firmly enough, and with sufficient speed and convenience, to makethe aforesaid precision attainable at practical production rates.

There has long been a problem in achieving cutting of non-ferrous sheetmaterial to precision tolerances. By precision tolerances is meant atolerance of plus-orminus 0.005 inch but especially of plus-or-minus0.002 inch or better. Such tolerances are, of course, known to beobtainable in machining such non-ferrous materials as aluminum sheet,asbestos board, and the like. Nevertheless, the apparatus heretoforeavailable for such precision cutting has not been feasible for use inmany cutting jobs because of the ineffective use of conventional clampmeans. The clamp means heretofore utilized have either allowed slippagewhich rendered the cutting process imprecise or have taken so much timeto operate that any economic advantage of obtaining high precisioncutting was restricted to processing a relatively high-priced workproduct. Consequently jobbers in the cutting of non-ferrous materialshave not been able to deliver a high-precision product at a desirablylow price. This general problem is particularly evident with respect torelatively small orders of highprecision sheet material.

Heretofore unrelated art concerns the finish of a sawcut edge and howquickly that finish is likely to deteriorate with prolonged use of priorart saw teeth. In general, applicants ability to produce precision-cutnonferrous articles will be understood to allow a customer to avoid anypost-cutting machining operations on these articles. Theprecision-machined part will be ready for use as delivered. In manysituations, however, the part will be subjected to a surface treatment,say anodizing, or the like and will require a good finish, say a finishof 63 root mean square (rms) or below. Presently-available saws whichwill provide this finish initially will provide a deteriorating resultwith time; that is after a days operation the finish of the cut edge maybe as high as 100 rms or more. This obviously presents a problem tomanufacturers who wish to produce an excellently finished, precision-cutworkpiece without excessive blade-changing or post-cutting buffingsteps.

SUMMARY OF THE INVENTION Therefore it is an object of the invention toprovide improved apparatus for precision cutting of sheet material.

Another object of the invention is to provide apparatus comprising novelclamp means for holding a workpiece being subjected to a precise cuttingoperation.

Further objects of the invention are to provide a novel clamp meanswhich is readily clamped and unclamped, to provide a novel clamp meanswhich engages snugly the workpiece even though the workpiece itselfcomprises dimensional irregularities, and to provide a clamp means whichsuccessfully clamps the workpiece against movement induced or allowed bythe cutting of the workpiece.

Still another object of the invention is to provide a saw whichcomplements the high precision cutting operation by allowing theoperation to produce articles having a superior finish on cut edgesthereof.

A further object of the invention is to provide improved means foradvancing the workpiece to be cut.

Another object of the invention is to provide a novel and relativelyinexpensive means for accurately advancing the workpiece into thecutting path of the saw.

Other objects of the invention will be obvious to those skilled in theart on reading the instant application.

The invention relates to a cutting apparatus having a work table, twoadjacent perimeters of which are bordered by workpiece guide railsequipped with means for sensing the proximity of the workpiece to theguide rail at a plurality of positions therealong and, consequently,allowing a quick determination of the square ness (or any predeterminedangle) of a piece to be cut and also allowing a means for detecting anydrift of positioning during the cutting operation. A workpiece clampmeans comprising elongate clamp members closely spaced, one along eachside of a cutting means and adapted to clamp the workpiece against thework table, is an important feature of the invention.

In the most favorable forms of the invention, the clamp bars comprisebiasing means associated therewith whereby gaps which would ordinarilyprevent snug, clampingcontact with the clamp bar are bridged by thebiasing means. Thus the biasing means is advantageously an active" meansin that it depends from, and contacts the workpiece below, the normalclamping surface of the clamp bar. Moreover, in the most favorableembodiments of the invention, a plurality of biasing means are arranged,not only along the direction of the cut for a distance which issubstantially coextensive with the travel path of the cutting means, butalso at right angles to the cut, i.e. on both sides of the travel pathof the cutting means.

The actuation means for the clamp should be adapted to provide avariable clearance between work table and the clamp. This is bestachieved by mounting the clamp for vertical movement and moving it byhydraulic means, mounted beneath the work table, and through a pair ofball bushings mounted proximate each end of the clamp. The clampactuator is a constant pressure device.

Non ferrous sheet material can be finished to excellent tolerance on theapparatus of the invention. Indeed, even where tolerances ofplus-or-minus 0.002 inch are required, say on a nominal /s-inch thickaluminum sheet, the apparatus can quickly and efficiently be used toturn out the sheet.

In order to give the cut edge of such a sheet a more finished"appearance, applicant has also constructed a saw means useful with theapparatus of the invention. In this improvement, finishing teethcomprising narrow flat bands, substantially vertical (i.e. radial) andtapered from the front face to the back face of the tooth, have beenfound to yield a finish along a cut edge which can be used suitably in awide variety of applications without further finishing operations. Thefinish attainable with this saw is markedly superior both with respectto the finish initially obtainable and with respect to the rate ofdeterioration of the finish of the cut edge of the workpiece with use ofthe saw. For example, the

cut edge will have a finish of as low as 16 rms initially and is usuallyin the 30 rms range for non-ferrous metals such as aluminum and itscommon alloys. More importantly, an initially attained finish of, say 24rms will not deteriorate substantially during the same period when useof a similar saw, not comprising the finishing tooth modificationdisclosed herein, would result in a deterioration of from 63 rms toabout 120 rms.

Without being bound by the hypothesis, it is believed by the inventorthat the advantage of his saw is the use ofa friction inducing surfacewhich is substantially par allel along the radius of the saw blade tothe workpiece edge being cut. The work created by this frictionalcontact of the surface is believed to have a substantial effect onsmoothing the surface.

As will be further explained below, the high tolerance work achieved bythe apparatus of the invention requires an even advance of the workpieceto the desired position along the linear cutting path of the saw blade.This advance has been achieved by mounting an adjustable rail formovement on two ball screw advance devices, wherein the ball screws areselected to have a close relative tolerance one to the other. Althoughit has been the custom in the mechanical arts to use screws machined toa particular tolerance in such situations, the inventor has discoveredthat standard ball bearing screws can be utilized at a great savings incost. This is achieved by making both advance ball screws by cuttingthem from a single screw stock, preferable discarding several inchesfrom the end of each such single screw. The resulting pair of screwswill have veryhigh relative tolerance despite the fact the manufacturersabsolute tolerance would forbid the indiscriminate use of any twoseparate commercially-obtained screws. Thus instead of using ground ballscrews with tolerances such as 0.0005 inches per foot, applicant can usea thread rolled ball screw with a tolerance of 0.001 inch per inch. Thisprocedure saves several hundreds of dollars in manufacturing eachmachine.

ILLUSTRATIVE EXAMPLE OF THE INVENTION In this application andaccompanying drawings there is shown and described a preferredembodiment of the invention and suggest various alternatives andmodifications thereof, but it is to be understood that these are notintended to be exhaustive and that other changes and modifications canbe made within the scope of the invention. These suggestions herein areselected and included for purposes of illustration in order that othersskilled in the art will more fully understand the invention and theprinciples thereof and will be able to modify it and embody it in avariety of forms, each as may be best suited in the condition of aparticular case.

IN THE DRAWINGS FIG. 1 is a perspective view ofa cutting machineconstructed according to the invention.

FIG. 2 is a fragmentary plan view of a machine similar to that shown inFIG. 1 and showing the work table and saw-travel path.

FIG. 3 is a side view of the work table and clamp actuating device asviewed along the line 3-3 of FIG. 2.

F 4 is a view of the work table and clampactuating mechanism as viewedalong the line 4-4 of FIG. 5A is a fragment of the clamp bar of Fl 5showing more detail thereof. 1

FIGS. 6 and 7 diagrammatically illustrate a novel finishing saw usefulwith the apparatus of the invention. 1 FIG. 8 shows the construction ofa saw-guard and how it co-operates with the movementofverticallyadjustable clamping means.

Referring toFIG. 1, it is seen that cutting machine 12 is mounted onframe 14 and comprises a work table 16 and a hood-enclosed saw 18adapted for movement with saw drive motor 19 across work table 16 onball bushings 21 along support rods 20. Rods are typically constructedof steel 2 inches in diameter and supported on brackets 22 attached toframe 14. Also attached to frame 14 is an electric control box 24.Progress of saw 18 across the work table is dependent on the speed atwhich feed screw 25 is turned by a variable drive feed screw motor notshown on the drawings.

Mounted proximate work table 16 are two workpiece. positioning railsmounted at a right angle to one another. Adjustable positioning rail ismounted on ball screws 32 by means of brackets 39 and in guide member 33for controlled movement of rail 30 against a workpiece (not shown on thedrawing, but understood by those skilled in the art to rest on slats 34and slats 35 of table 16. See FIG. 4 for the position of slats 35.).Stationary positioning rail 31 is mounted along one edge of table 16 ata right angle to rail 30. Ball screws I and a dial 42. Probes 40 arepositioned to engage.

the edge of a workpiece when it is flat against the rails 30 and 31.Sensing probes 40 conveniently extend about 0.020 inches from rails 30and 31 when in normal position. The dial indicator is. convenientlycalibrated to a 0.020 inch scale per revolution.

A clamp bar 50, best seen in FIGS. '5 and 5A, extends across table 16.Clamp bar comprises two elongate clamping members 52, one on each sideof the path of travel 54 of the cutting means, saw 18. Each clamp bar 52comprises a plurality of independent biasing means, i.e. springs 56,mounted in receptacles 58 within clamp bars 52. Springs 56 are affixedwith epoxy adhesive 58- at one end thereof.

Each clamping member 52 comprises an elongate recess 62 which providesclearance for saw guide means.

as it travels along clamp bar 52. The clamping member is preferablyunitary, that is integrated into a single structural unit as is shown inFIG; 5. One spring biasing means suitable for many purposes would be asteel spring constructed of 0.094 wire, 1 inch long, 0.5 inch indiameter and exerting about 15 pounds force when compressed about 0.050inches by clamping means shown in FIGS. 3 and 4.

Clamping member 52 is actuated for vertical clamping movement by meansof bracket 68 and a flanged cartridge i.e. collar, 69. Clamp-actuationassembly 66 connected between clamp bar and ball bushing shaft 72 via avertically slideablc ball bushing post member 73 which is snugly clampedbetween members 52.

Shaft 72 comprises cam rollers 74 at either end thereof; these fittinginto a slot at 71in'meinber 73 so that they may turn freely. Shaft 72is, in turn, connected via a lever arm member 76 to a pivot shaft 78.Lever arm 76 comprises, is welded to operating shaft 72 and pivot shaft78 respectively. Shaft 78 is pivotally mounted in collars 69. Force isapplied to arms 76 via shaft piston rod 80 of hydraulic cylinder 82acting through clevis-type connector 84. Cylinder 82 is pivotallymounted at pivot 86.

In FIG. 8 is illustrated schematically one means whereby a saw housing88 is made to accomodate the movement of clamping member 50. Twomoveable side shields 90 are held in slots 92 and move freely up anddown therein in response to the vertical movement of member 50.

FIGS. 6 and 7 illustrate, somewhat schematically, cutting means which isparticularly useful with the apparatus of the invention. In FIG. 6, arotary saw is mounted for rotation by motor 19 on the shaft 102 ofcutting machine 12. The saw is carbide tipped and of a generallyconventional design, i.e. it has roughing teeth 104 and finishing teeth106 alternately arranged along the periphery thereof. Only a few teethare shown in FIG. 6, this being sufficient to illustrate this aspect ofthe invention. Roughing teeth 104 rise somewhat higher from the outercircumference 108 of the circular portion of saw 100. These roughingteeth '104 are of conventional design. 7

The particular improvement of the inventor is related to the use inconjunction with said roughing teeth, of novel finishing teeth. Asindicated in FIG. 7, finishing tooth 106 comprises a generally taperedmember 110, the taper being such that angles 111 are about 3 to 5,although they may be from 1 to 10 depending upon the relative propertiesof the saw and the material to be cut. Along the top of each lateralfaces 1 12 proximate top face 114 is a substantially vertical levelledface 115 defined by two edges 116. These faces 115 run the full lengthof finishing tooth 106, i.e. about 0.35 inches, and are about 0.030inches in width. The faces are advantageously between 0.1 and 0.01inches in width. These dimensions are particularly suited for cutting ofsuch non-ferrous metals as alluminum.

In operation, or the apparatus, a workpieceis placed on worktable 16 andbrought snugly against rails 30 and 31. This, of course, assumes agenerally rectangular workpiece since the angle between rails 30 and 31is a 90 angle in the illustrative example of the drawings. Assuming allindicators are properly calibrated and the angle of the workpiece isperfectly square, all indicator dials will read the same. However, tothe extent that the workpiece is out of square or has other defects likesizeable burrs, they immediately become evident. Thus the piece can besquared" before proceeding further or, if a single side is imperfect,the fault side can be selected to be the side removed during the cuttingoperation.

Once the operator is assured the workpiece is in condition to proceed,and in the proper position relative to saw path 54, he causes cylinder82 to retract about 2 inches and thereby causes arm 76 to pivot down.Thereupon clamp bar 50 bears down on the workpiece on each side oftravel path 54. The workpiece is supported on slats 35,-the sawtravelling between such slats as seen in FIG. 2.

Springs 56 are typically placed about l-inch apart along, say, a 20-inchlength of the clamp bar. If just compressed to the edge of theirhousings, these springs will exert a minimum of about 600 pounds ofpressure. Normally, however, the clamping pressure will exceed thisconsiderably and the only springs that will be effective in the clampingaction will be those which protrude outside of receptacles 58 to engagea surface which, for some reason, doesnot contact a main bearing surfaceof clamp bar 50. i

When the workpiece is properly clamped, the sawing can be carried out,and the proper positioning of the workpiece can be visually monitored asthe sawing progresses.

Among the modifications which can be made in the illustrated apparatusis the substitution of various elongate biasing means for one or both ofthe illustrated series of springs. One' desirable substitute would be anelongate strip or elastomeric material, e.g. a distortable syntheticrubber such as chloroprenega nitrile rubber, or an elastomeric siliconeresin material. Such a strip would have the advantage of being incontinual contact along the portion of the workpiece being processed.Another useful biasing means is a fluid containing balloon which couldbe expanded by the use of either water or gas to achieve the desirableclamp pressure on portions of the workpiece that do not fit snuglyagainst the main bearing surface of the clamp bar.

It will be understood that a single clamp bar can comprise one or moresuch biasing means.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

I claim:

1. A clamp for holding a workpiece firmly against a work table andthereby to enable the precision cutting of said workpiece, said clampcomprising A. two elongate clamp members defining a slot between saidclamp members said slot adapted to form a travel path for a cuttingtool;

B. A plurality of downwardly extending biasing means arranged along thelength of each said clamp member, said biasing means adapted to providemeans for biasing said clamp and said workpiece to assure clampingcontact of said workpiece against said work table;

C. means to raise said clamp vertically from said work table to providea variable clearance between said table and said clamp, and

D. means to maintain substantially constant clamping pressure on saidclamp at variable clearances from said table.

2. Apparatus as defined in claim 1 wherein said biasing means exert aminimum of 600 psig.

3. A clamping apparatus as described in claim 1 comprising additionallya saw housing comprising two moveable side shields adapted to be movedfreely up and down in response to the vertical movement of said clamp.

4. A clamp as defined in claim 1 wherein said means for raising andlowering said clamp members with respect to said table are actuated byforce applied proximate to each end of said clamp members, and whereinsaid means for raising and lowering said clamp mem-' bets comprise:

a. post members connected to said clamp members proximate to each endthereof, each of said post members comprising a slot therein,

b. ball bushings mounted on said table and forming means to receive, forslideable vertical movement therein, each of said post members,

0. means to vertically move said post members thereby, adapting saidclamp members to clamp and unelamp said object and wherein,

i. said means to vertically move said post comprising l. lever means and2. cam rollers positioned for rotation in said slots of said post, saidcam rollers, forming means to transmit force to said post members onactuation of said lever means.

5. Apparatus as defined in claim 1 wherein said .biasing means comprisea series of apertures, each having a spring connected within, eachspring normally protruding from its associated aperture, therebyproviding a biasing means which has no substantial effect when saidsprings are compressed into said apertures,

6. Apparatus as defined in claim 5, wherein said biasing means exert aminimum of 600 psig.

7. A clamp as defined claim 5 wherein said means for raising andlowering said clamp members with respect to said table are actuated byforce applied proxi: mate to each end of said clamp members, and whereinsaid means for raising and lowering said clampmeans comprise: v I I a.post memberscpnnected to said clamp members proximate each end thereof,each of said post .members comprising a slot therein,

therein, each of said postmembers, c. means to vertically move said postmembers thereby, adapting said clamp members to clamp,-

and unclamp said object and wherein,

i. said means to vertically move said post comprise ing 1. lever meansand 2. cam rollers positioned for rotation in said slots of said post,said cam rollers forming meansto transmit force to said post members onactua-

1. A clamp for holding a workpiece firmly against a work table andthereby to enable the precision cutting of said workpiece, said clampcomprising A. two elongate clamp members defining a slot between saidclamp members said slot adapted to form a travel path for a cuttingtool; B. A plurality of downwardly extending biasing means arrangedalong the length of each said clamp member, said biasing means adaptedto provide means for biasing said clamp and said workpiece to assureclamping contact of said workpiece against said work table; C. means toraise said clamp vertically from said work table to provide a variableclearance between said table and said clamp, and D. means to maintainsubstantially constant clamping pressure on said clamp at variableclearances from said table.
 2. cam rollers positioned for rotation insaid slots of said post, said cam rollers forming means to transmitforce to said post members on actuation of said lever means.
 2. camrollers positioned for rotation in said slots of said post, said camrollers, forming means to transmit force to said post members onactuation of said lever means.
 2. Apparatus as defined in claim 1wherein said biasing means exert a minimum of 600 psig.
 3. A clampingapparatus as described in claim 1 comprising additionally a saw housingcomprising two moveable side shields adapted to be moved freely up anddown in response to the vertical movement of said clamp.
 4. A clamp asdefined in claim 1 wherein said means for raising and lowering saidclamp members with respect to said table are actuated by force appliedproximate to each end of said clamp members, and wherein said means forraising and lowering said clamp members comprise: a. post membersconnected to said clamp members proximate to each end thereof, each ofsaid post members comprising a slot therein, b. ball bushings mounted onsaid table and forming means to receive, for slideable vertical movementtherein, each of said post members, c. means to vertically move saidpost members thereby, adapting said clamp members to clamp and unclampsaid object and wherein, i. said means to vertically move said postcomprising
 5. Apparatus as defined in claim 1 wherein said biasing meanscomprise a series of apertures, each having a spring connected within,each spring normally protruding from its associated aperture, therebyproviding a biasing means which has no substantial effect when saidsprings are compressed into said apertures.
 6. Apparatus as defined inclaim 5, wherein said biasing means exert a minimum of 600 psig.
 7. Aclamp as defined in claim 5 wherein said means for raising and loweringsaid clamp members with respect to said table are actuated by forceapplied proximate to each end of said clamp members, and wherein saidmeans for raising and lowering said clamp means comprise: a. postmembers connected to said clamp members proximate each end thereof, eachof said post members comprising a slot therein, b. ball bushings mountedon said table and forming means to receive, for slideable verticalmovement therein, each of said post members, c. means to vertically movesaid post members thereby, adapting said clamp members to clamp andunclamp said object and wherein, i. said means to vertically move saidpost comprising